Polymer film splicing method and device, and stretching method

ABSTRACT

An off-line stretching device includes a film supply chamber, a tenter section, a relaxation chamber, a cooling chamber, and a winding chamber. The film supply chamber includes a splicing section, where a rear end of a preceding film and a front end of a trailing film are overlapped to be spliced to each other by thermal welding. The thermal welding is performed from above and below the film while a temperature of welding heads of a heat sealer, contacting with the film, is kept at a level equal to or less than a decomposition temperature of the preceding and trailing films. The spliced film is stretched in the tenter section and subjected to heat treatment for stress relaxation in the relaxation chamber, to shrink in a film width direction. Since the shrinkage amount of a spliced area and that of a peripheral area become equal to each other, the occurrence of wrinkles in the spliced area and tears of the film in the peripheral area can be prevented. Additionally, since a heat transfer distance between a film surface and a film splicing surface can be shortened, the heating from above and below the film enables high-speed welding.

FIELD OF THE INVENTION

The present invention relates to a polymer film splicing method anddevice, and a polymer film stretching method.

BACKGROUND OF THE INVENTION

Recently, in accordance with rapid development and popularization ofliquid crystal display (LCD) or the like, the demand for a celluloseester (cellulose acylate) film, in particular, a triacetyl cellulose(TAC) film used as a protective film for the LCD or the like, has beenincreasing. According to the increase in the demand for the TAC film,the improvement in productivity thereof has been desired. The TAC filmis produced as follows. A dope containing the TAC and a solvent is castthrough a casting die onto a support continuously moving to form acasting film thereon. The casting film is dried or cooled to besolidified. The solidified casting film is peeled from the support toform a wet film. The wet film is dried and wound as a film. According toa solution casting method described above, it is possible to form a filmcontaining less foreign materials and having more excellent opticalproperties in comparison with a film forming method by melt-extrusion.

In the solution casting method, as the support onto which the dope iscast, a band and a drum are used. The drum can achieve improvement in acasting speed more readily in comparison with the band. In order tosolidify the casting film on the support, the casting film is dried, orcooled so as to turn into gel. Additionally, in order to adjust theoptical properties of the TAC film, in particular retardation thereof,the TAC film is stretched.

The optimum film producing speed and the optimum stretching speed aredifferent from each other. The film producing speed requires more timethan the stretching speed. Therefore, in the case that the stretchingspeed is adjusted in accordance with the film producing speed, it isimpossible to stretch the film enough to improve the optical properties.Accordingly, it is proposed that the film is stretched in an off-linemanner independently from a solution casting line (see Japanese PatentApplication Laid-open No. 2002-311240, for example).

In a case where the film is stretched in an off-line mannerindependently from the solution casting line as disclosed in JapanesePatent Application Laid-open No. 2002-311240, for the purpose ofefficiently performing the stretching process, the TAC film ispreferably stretched continuously. In this case, in order to supply thefilm continuously, a portion in which a rear end of a preceding polymerfilm and a front end of a trailing polymer film are overlapped with eachother is heated to be welded. Thereby, the preceding film and thetrailing film are spliced to each other (see Japanese Utility ModelApplications Laid-open No. 53-020268 and 53-051864, for example).

However, as disclosed in Japanese Utility Model Applications Laid-openNo. 53-020268 and 53-051864, when a heater is disposed above or belowthe portion in which the preceding and trailing polymer films areoverlapped with each other, in the case that the temperature of theheater is raised or in the case that the contact time between the heaterand the film is increased for the purpose of enhancing the welding, thetemperature of the heated film exceeds the degradation temperature ofthe polymer in the film in some cases. The polymer film, in particular,cellulose ester film has the melting point of 300° C. and thedecomposition temperature of more than 300° C. Since the melting pointand the decomposition temperature are close to each other, in the casethat the welding temperature is set higher for the purpose of weldingthe film sufficiently, pitting occurs on the welded portion of thepolymer films or the degradation of the polymer proceeds due to theoverheating of the polymer film. Accordingly, there is a problem that itis impossible to achieve sufficient splicing strength.

In an off-line stretching device, the TAC film is subjected to asplicing process for splicing a preceding film and a trailing film, astretching process for stretching the spliced TAC film by holding theside ends thereof with use of plural clips in a film width directionwhile heating the TAC film continuously transported, and a relaxationprocess for subjecting the TAC film thus stretched to heat treatment forstress relaxation (for example, see U.S. application serial number No.12/058,631 corresponding to Japanese Patent Application No.2007-084424). In the splicing process, as an easy splicing device, asingle-sided splicing tape is used. In general, the single-sidedsplicing tape has a sheet as a base and an adhesive layer formed on onesurface of the base. The base material of the base is different fromthat of the TAC film.

Further, the TAC film subjected to the stretching process and heattreatment for stress relaxation in the off-line stretching deviceshrinks in the film width direction after the heat treatment for stressrelaxation. The thermal shrinkage amount of the base of the single-sidedsplicing tape and the thermal shrinkage amount of the film are differentfrom each other. Therefore, as shown in FIG. 11, in the case that apreceding film 3 a and a trailing film 3 b are overlapped with eachother and a single-sided splicing tape 60 is adhered thereon so as toextend in a film width direction B in order to splice the preceding film3 a and the trailing film 3 b, the shrinkage amount of a spliced area 61is larger than that of an area around the spliced area 61 (peripheralarea). As a result, wrinkles 62 occur in the spliced area 61.

When the wrinkles 62 occur in the spliced area 61, the wrinkles 62 alsooccur in the peripheral area. The area having the wrinkles 62 can not beused as a product and need to be discarded. Therefore, there is aproblem that the area as a product is decreased. Further, in some cases,the TAC film breaks due to the occurrence of wrinkles 62, thus causing aproblem. The above-described problems are not limited to the TAC film,and also applied to other polymer films.

Accordingly, there is a problem that it is not possible to obtainsufficient splicing strength in the case that the splicing is performedby welding, and further wrinkles occur on the film which is subjected towelding, splicing, stretching, and the heat treatment for stressrelaxation.

SUMMARY OF THE INVENTION

To solve the above problems, a first object of the present invention isto provide a splicing method and device for more infallibly splicingpolymer films by thermal welding even though the polymer film such ascellulose ester film is easily thermally decomposed. A second object ofthe present invention is to provide a polymer film stretching methodcapable of preventing occurrence of wrinkles in a film spliced areaafter a heat treatment for stress relaxation.

To achieve the first object, according to the present invention, thereis provided a splicing method of a polymer film including the steps of:overlapping a rear end of a preceding polymer film and a front end of atrailing polymer film; pressing welding heads against a portion in whichthe preceding and trailing films are overlapped with each other fromeach side in a film overlapping direction while sandwiching the portionbetween the welding heads; and welding the films while keeping atemperature of the welding heads contacting the film at a temperatureequal to or less than a decomposition temperature of the polymer film,to splice the rear end and the front end to each other. Note that thepolymer film may be a cellulose ester film.

Further, according to the present invention, there is provided asplicing device of a polymer film including: a welding head provided ateach side of a portion in which a rear end of a preceding polymer filmand a front end of a trailing polymer film are overlapped with eachother in a film overlapping direction; a shifter for moving the weldingheads in the film overlapping direction between a pressing position anda retracted position, the welding heads sandwiching and pressing aportion in which the preceding and trailing films are overlapped witheach other in the pressing position, and the welding heads beingretracted from the pressing position in the retracted position; and aheating controller for heating the welding heads contacting thepreceding and trailing film at a temperature equal to or less than adecomposition temperature of the polymer film after the welding heads isshifted to the pressing position by the shifter. Note that the polymerfilm may be a cellulose ester film.

According to the film splicing method of the present invention, theportion in which the preceding and trailing films are overlapped witheach other is heated from both sides, and therefore it is possible toshorten the heat transfer distance between the film surface and the filmsplicing surface. Further, while the temperature of the portion in whichthe preceding and trailing films are overlapped with each other is keptat a level equal to or less than a decomposition temperature of thefilm, the overlapped portion can be welded. Accordingly, it is possibleto surely perform high-speed welding of the films each having a meltingpoint and decomposition point close to each other such as a polymerfilm, in particular, cellulose ester film while preventing occurrence ofpitting.

Additionally, since it is possible to shorten the heat transfer distancebetween the film surface and the film splicing surface, it is alsopossible to decrease heating amount for the welding. Thereby,electricity supplied to the heater can be decreased to achieveimprovement in energy conservation.

To achieve the second object, according to a polymer film stretchingmethod of the present invention, a portion in which a rear end of apreceding polymer film and a front end of a trailing polymer film areoverlapped with each other is welded. Thereby, the preceding film andthe trailing film are spliced to each other. The spliced polymer filmsare continuously transported. Side ends of the spliced polymer film areheld with use of plural clips to be stretched in a film width directionwhile the polymer film is being heated. While being continuouslytransported, the stretched polymer film is subjected to a heat treatmentfor stress relaxation such that a shrinkage amount of a spliced area ofthe preceding and trailing polymer films and a shrinkage amount of anarea around the spliced area are approximately equal to each other inthe film width direction. Note that the welding is performed with use ofheat caused by an ultrasonic splicer or a heat sealer, or a polymersolvent.

Further, according to a polymer film stretching method of the presentinvention, a splicing tape having an adhesive layer and no base isadhered to a portion in which a rear end of a preceding polymer film anda front end of a trailing polymer film are overlapped with each other.Thereby, the preceding film and the trailing film are spliced to eachother. The spliced polymer films are continuously transported. Side endsof the spliced polymer film are held with use of plural clips to bestretched in a film width direction while the polymer film is beingheated. While being continuously transported, the stretched polymer filmis subjected to a heat treatment for stress relaxation such that ashrinkage amount of a spliced area of the preceding and trailing polymerfilms and a shrinkage amount of an area around the spliced area areapproximately equal to each other in the film width direction.

According to the polymer film stretching method of the presentinvention, the portion in which the rear end of the preceding polymerfilm and the front end of the trailing polymer film are overlapped witheach other is welded, and thereby the preceding film and the trailingfilm are spliced to each other, such that the shrinkage amount of thespliced area of the preceding and trailing polymer films and theshrinkage amount of the area around the spliced area after the heattreatment for stress relaxation are approximately equal to each other inthe film width direction. Therefore, after the heat treatment for stressrelaxation, no wrinkles occur in the film spliced area and no tearsoccur in the area around the spliced area.

Additionally, according to the polymer film stretching method of thepresent invention, the preceding film and the trailing film are splicedwith use of the double-sided adhesive tape having the adhesive layer andno base such that the shrinkage amount of the spliced area of thepreceding and trailing polymer films and the shrinkage amount of thearea around the spliced area after the heat treatment for stressrelaxation are approximately equal to each other in the film widthdirection. Therefore, after the heat treatment for stress relaxation, nowrinkles occur in the film spliced area and no tears occur in the areaaround the spliced area.

BRIEF DESCRIPTION OF THE DRAWINGS

One with ordinary skill in the art would easily understand theabove-described objects and advantages of the present invention when thefollowing detailed description is read with reference to the drawingsattached hereto:

FIG. 1 is a plan view illustrating an off-line stretching deviceaccording to an embodiment of the present invention;

FIG. 2 is a plan view illustrating a preceding film, a trailing film,and a heat sealer;

FIG. 3 is a perspective view illustrating the preceding film, thetrailing film, and welding heads;

FIG. 4 is a side view illustrating a procedure of a welding process withuse of the welding heads;

FIG. 5 is a view illustrating the preceding film and the trailing film;

FIG. 6 is a plan view illustrating a tenter section;

FIG. 7 is a front view illustrating a clip;

FIG. 8 is a side view illustrating an ultrasonic splicer;

FIG. 9 is a perspective view illustrating the preceding film whose rearend is coated with acetone, and the trailing film;

FIG. 10 is a perspective view illustrating the preceding film, thetrailing film, and a double-sided splicing tape; and

FIG. 11 is a view illustrating a film subjected to a stretching processand heat treatment for stress relaxation in a conventional manner.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention are described hereinbelow. Thepresent invention, however, is not limited to the following embodiments.

Embodiment 1

As shown in FIG. 1, an off-line stretching device 2 is used forstretching a TAC film 3 (hereinafter referred to as film 3), andincludes a film supply chamber 4, a tenter section 5, a relaxationchamber 6, a cooling chamber 7, and a winding chamber 8 disposed in thisorder from a upstream side along a film transporting direction A. A filmroll 9 produced in a solution casting apparatus is loaded in the filmsupply chamber 4. The film roll 9 is obtained by winding the film 3around a core in a roll manner. The film 3 is fed from the film roll 9loaded in the film supply chamber 4 to the tenter section 5. In thetenter section 5, the film 3 is continuously stretched in a film widthdirection while being heated. The stretched film 3 passes through therelaxation chamber 6 and the cooling chamber 7 to be cooled. The cooledfilm 3 is wound in the winding chamber 8. In the tenter section 5, thefilm 3 is stretched in the film width direction by 100.5% to 300%. Ineach of the film supply chamber 4, the tenter section 5, the relaxationchamber 6, the cooling chamber 7, and the winding chamber 8, there isprovided an edge position controller (EPC) (not-shown) for controllingsuch that the film 3 is transported in a precise manner withoutmeandering.

The film supply chamber 4 includes a turret-type film feeding device 10and a splicing section 11. The film feeding device 10 includes a turretarm 13 provided with a mounting shaft 12 at each end. The film roll 9 isloaded to each of the mounting shafts 12. The turret arm 13 makes half arotation intermittently. In the intermittent rotation by 180°, one ofthe mounting shafts 12 is set at a film feeding position 16 (at a sideof the splicing section 11), and the other thereof is set at a corereplacement position 17. The film 3 is fed to the splicing section 11from a film roll 9 mounted to the mounting shaft 12 located at the filmfeeding position 16. When the film 3 located at the film feedingposition 16 is used up, the turret arm 13 rotates, and an empty roll isremoved from the mounting shaft 12 located in the core replacementposition 17, and then a new film roll 9 is mounted thereto. Uponcompleting feeding of the film 3 from the film roll 9 loaded to themounting shaft 12 located at the film feeding position 16, the turretarm 13 rotates by 180° to set the film roll 9 loaded to the othermounting shaft 12 at the film feeding position 16, thus feeding the film3. Concurrently, the rear end of the preceding film 3 a fed first andthe front end of the trailing film 3 b fed from the new film roll 9 arespliced to each other in the splicing section 11.

A reservoir 29 is disposed between the film supply chamber 4 and thetenter section 5 to constitute a loop of the film 3 having a lengthlonger than the length necessary for the film splicing, process.Accordingly, since the film 3 housed in the reservoir 29 is fed to thetenter section 5 at the time of splicing the preceding film and trailingfilm, it is possible to perform the splicing process of the film 3without stopping the operation of the tenter section 5.

As shown in FIG. 2, the splicing section 11 includes a support roller 51for supporting the preceding film 3 a and a support roller 52 forsupporting the trailing film 3 b. In order to supply the film 3continuously to the tenter section 5, in the splicing section 11, a rearend of a preceding film 3 a fed in first and a front end of a trailingfilm 3 b fed following the preceding film 3 a are overlapped with eachother to be spliced by thermal welding with use of a heat sealer 20.(Not that, welding means melting and connecting the films by applyingheat.) As shown in FIG. 4A, for example, the heat sealer 20 includes anupper welding head 21 and a lower welding head 22 provided so as tosandwich a transporting path of the film 3 therebetween. The upperwelding head 21 has a heater 23 exposed from its lower surface, and thelower welding head 22 has a heater 24 exposed from its upper surface. Ashift mechanism 56 causes each of the upper welding head 21 and lowerwelding head 22 to move between a heating position and a retractedposition. The heaters 23 and 24 are caused to contact with the film 3 atthe heating position. The heaters 23 and 24 are caused to be retractedfrom the film 3 at the retracted position. The temperature of each ofthe heaters 23 and 24 is controlled by heat controllers 25 and 26 andsensors (not shown) respectively.

As shown in FIG. 3, the splicing section 11 includes four supportrollers 51, 52, 71, and 72. The number of the support rollers is notlimited four, and any number of support rollers may be provided as longas they can support the film. As shown in the drawing, the width of eachof the support rollers 51, 52, 71, and 72, and the welding heads 21 and22 is made longer than that of the film 3 to be transported.

The process for splicing the preceding and trailing films with use ofthe heat sealer 20 is described hereinafter. FIG. 4 shows a procedure ofwelding the portion in which the preceding film 3 a and the trailingfilm 3 b are overlapped with each other with use of the welding heads 21and 22. FIG. 4A shows a state in which the preceding film 3 a passesthrough the splicing section 11. When the feeding of the film 3 a fromthe film roll 9 is finished as shown in FIG. 1, the rear end of thepreceding film 3 a is stopped at the welding position (also referred toas heating position) of the splicing section 11 as shown in FIG. 4B. Theupper welding head 21 is located above the welding position, and thelower welding head 22 is located below the welding position.

Next, in the film feeding device 10 shown in FIG. 1, the new film roll 9is set at the film feeding position 16, and the trailing film 3 b is fedtherefrom. After the rear end of the preceding film 3 a and the frontend of the trailing film 3 b are overlapped at the welding position, asshown in FIG. 4C, the feeding of the trailing film 3 b is stopped.

Next, as shown in FIG. 4D, the upper welding head 21 moves downwards andthe lower welding head 22 moves upwards, to sandwich the portion inwhich films 3 a and 3 b are overlapped with each other therebetween. Inaccordance with that, each of the heaters 23 and 24 is set to apredetermined temperature by the temperature controller 25 and 26. Thetemperature is set such that the film 3 is welded but not decomposed,for example, within the range of 150° C. to 299° C. The portion in whichthe films 3 a and 3 b are overlapped with each other is heated by thewelding heads 21 and 22 respectively provided above and below theportion, and the portion is partially melted to be spliced with eachother, to form the welded portion (spliced area) 28. The portion isheated for a desired period of time, and thereafter the heating isstopped. The portion is naturally cooled while being nipped therebetweenfor a desired period of time. Thereby, the rear end of the precedingfilm 3 a and the front end of the trailing film 3 b are spliced witheach other on the welded portion 28. Note that instead of naturalcooling, a cooling device may be provided at each of the welding heads21 and 22 in order to cool the overlapped portion in a press-contactmanner.

Next, as shown in FIG. 4E, the upper welding head 21 moves upwards andthe lower welding head 22 moves downwards, and thereby both weldingheads 21 and 22 are respectively set to the retracted position away fromthe welding position. Then, the films 3 a and 3 b start to be fed.

As described above, the portion in which the films 3 a and 3 b areoverlapped with each other is heated from both upper and lower sides,and therefore the heat transfer distance between the surface of theheated film and the film splicing surface can be shortened toapproximately half in comparison with a case where only one head is usedfor welding of the films in a conventional manner. Accordingly, thefilms can be welded while the temperature of the portion in which thefilms 3 a and 3 b are overlapped with each other is kept at a levelequal to or less than the decomposition temperature of the polymer.Additionally, it is also possible to prevent occurrence of pitting onthe welded portion and degradation of the polymer in the polymer filmhaving a melting point of the polymer and decomposition point thereofclose to each other.

Note that instead of using the welding heads 53 and 54 provided so as toextend along the film width direction, a pair of welding rollerscontaining heaters may be disposed so as to sandwich the portion inwhich the rear end of the preceding film 3 a and the front end of thetrailing film 3 b are overlapped with each other in a film overlappingdirection such that the pair of welding rollers are rolled in contactwith the overlapped portion in the film width direction. Note that, thefilm overlapping direction is a direction so as to sandwich the filmsfrom above and below in a vertical direction, as indicated by arrows Xin FIG. 2, for example.

In a case where the preceding and trailing films 3 a and 3 b are splicedto each other with use of the heat sealer 20 as shown in FIG. 5, in thefilm 3 subjected to the stretching process and a heat treatment forstress relaxation, a shrinkage amount of the spliced area 28 and ashrinkage amount of an area around the spliced area 28 (hereinafterreferred to as peripheral area) are equal to each other, and a width ofthe spliced area 28 after shrinkage (after heat treatment for stressrelaxation) and a width of the peripheral area after shrinkage becomeequal to each other. Note that the stretching process and the heattreatment for stress relaxation are described in detail later.

Further, in a case where the preceding and trailing films 3 a and 3 bare spliced to each other with use of the heat sealer 20 as describedabove, since different materials are not contained in the spliced area28, the spliced area 28 can be reused as a material of the film. Notethat, instead of the heat sealer 20, an impulse sealer can be used forthermal-welding and splicing of the films.

As shown in FIG. 6, in the tenter section 5, the film 3 is stretched inthe film width direction B while being transported in the filmtransporting direction A. The tenter section 5 includes a first rail 31,a second rail 32, a first chain (endless chain) 33 guided by the firstrail 31, and a second chain (endless chain) 34 guided by the second rail32.

The first chain 33 is bridged over a driving sprocket wheel 35 and adriven sprocket wheel 36, and the second chain 34 is bridged over adriving sprocket wheel 37 and a driven sprocket wheel 38. The drivingsprocket wheels 35 and 37 are disposed at a side of tenter outlet 66,and caused to rotate by a not-shown driver. The driven sprocket wheels36 and 38 are disposed at a side of tenter inlet 65.

The first chain 33 and the second chain 34 are provided with pluralclips 39 at a predetermined interval. While holding the side edges ofthe film 3, the clips 39 move along the rails 31 and 32, to stretch thefilm 3 in the film width direction B. The clips 39 start holding thefilm 3 at a point PA, and release the film 3 at a point PB. The clips 39start stretching the film 3 at a point PC, and finish stretching thefilm 3 at a point PD. Under the stretching process, the film width Wpaat the point PA, the film width Wpb at the point PB, the film width Wpcat the point PC, and the film width Wpd at the point PD satisfy aformula: Wpa=Wpc≦Wpd=Wpb. Although the stretching ratio of the film 3 isappropriately changed in accordance with the desired optical propertiesor the like, the film 3 is preferably stretched in the film widthdirection B by 100.5% to 300%.

The tenter section 5 is disposed in a drying chamber (not-shown). Thetenter section 5 is divided into a preheating zone 5 a, aheating/stretching zone 5 b, and a heat treatment for stressrelaxation/stretching relaxation zone 5 c in this order from thedownstream side in the film transporting direction A. The film 3 ispreheated while being transported with the film width kept at Wpa in thepreheating zone 5 a. The distance between the pair of clips 39 does notchange, and the film 3 is not stretched by the clips 39 in the filmwidth direction B. In the heating/stretching zone 5 b, the film 3 isheated, and the distance between the pair of clips 39 graduallyincreases from Wpc to Wpd. In the heat treatment for stressrelaxation/stretching relaxation zone 5 c, the film 3 is heated whilebeing transported with the film width kept at Wpd, to be subjected tothe heat treatment for stress relaxation, and the film 3 is stretched bythe clips 39 in the film width direction B. The distance between thepair of clips 39 gradually decreases or does not change, and the film 3is subjected to the stretching relaxation (heat treatment for stressrelaxation).

As shown in FIG. 7, the clip 39 consists of a clip main body 80 and arail attachment portion 81. The clip main body 80 consists of a frame 82having an approximately inverted U shape and a flapper 83. The flapper83 is rotatably mounted to the frame 82 by a mounting shaft 82 a. Theflapper 83 shifts between a film holding position (closed position) anda film releasing position. At the film holding position, the flapper 83stands approximately vertically. At the film releasing position, areleasing member 70 contacts with an engaging head 83 a and rotates inan oblique direction. The flapper 83 is generally biased under its ownweight or by a spring (not shown) so as to be set at the film holdingposition. The film 3 is held between a film holding surface 82 b and aflapper lower surface 83 b at the film holding position.

The rail attachment portion 81 consists of an attachment frame 84, andguide rollers 85, 86, and 87. The attachment frame 84 is provided withthe first chain 33 or the second chain 34. The guide rollers 85 to 87respectively contact with each support surface of the driving sprocketwheels 35 and 37 (see FIG. 6) or a support surface of the first rail 31or the second rail 32, and thereby rotates. As a result, the clip mainbody 80 does not fall from the driving sprocket wheels 35 and 37, andthe rails 31 and 32, and is guided along the first and second rails 31and 32.

The releasing member 70 of the clip 39 is disposed so as to be close tothe sprocket wheels 35 to 38 (see FIG. 6). At the driven sprocket wheels36 and 38 at the side of tenter inlet 65 (see FIG. 6), the releasingmember 70 contacts with the engaging head 83 a of the clip 39 to releasethe engaging head 83 a in front of the film holding position PA, andthereby the side ends of the film 3 can be transported to the tentersection 5. When the film 3 passes through the film holding position PA,the releasing member 70 moves away from the engaging head 83 a, and theclips 39 is moved away from the releasing position to be set at the filmholding position. Thus, the side ends of the film 3 are held. Similarly,at the driving sprocket wheels 35 and 37 at the side of the tenteroutlet 66, the clips 39 are set to the releasing position by thereleasing member 70 at the film releasing position PB, and thereby theholding of the side ends of the film 3 are canceled.

Returning to FIG. 1, the film 3 is stretched in the tenter section 5 andsent to a slitting device 40. The side edges of the film 3, which wereheld by the clips 39, are cut off at a predetermined cutting line by theslitting device 40, and the side edges thus cut away as slits are cutinto pieces by a cut blower 41. The side edges thus cut into pieces aresent to a crusher 42 by a not-shown blowing device and crushed intochips by the crusher 42. The chips are reused for preparing the dope,thus resulting in improvement in cost.

The side edges of the preceding film 3 a and the trailing film 3 b arereused. In a case where the preceding film 3 a and the trailing film 3 bare spliced with use of the splicing tape, it is necessary to remove thesplicing tape from the side edges to reuse the side edges. However, in acase where the preceding film 3 a and the trailing film 3 b are splicedwith use of the heat sealer 20, since the splicing section 11 containsno substances different from those of the film 3 and the splicingsection 11 can be reused in the material recycle, the edges in thespliced state can be used directly. Thus, it is possible to save troubleof removing the splicing tape at the time of reusing, and increaseoperability in recovering of the side edges. Further, it is possible tosimplify the structure of the off-line stretching device 2. The film 3whose side edges are cut away by the slitting device 40 is sent to therelaxation chamber 6.

The relaxation chamber 6 includes plural rollers 43, and the film 3 istransported by the rollers 43 in the relaxation chamber 6. Air at adesired temperature is blown to the relaxation chamber 6 by a blower(drying air duct) (not-shown) to subject the film 3 to heat treatmentfor stress relaxation. The temperature of the air is preferably in therange of 20° C. to 250° C. The temperature of the film 3 is graduallydecreased.

The film 3 subjected to the heat treatment for stress relaxation is sentto the cooling chamber 7 to be cooled to 30° C. or less, and then sentto the winding chamber 8. The winding chamber 8 includes a windingdevice 47 provided with a winding roller 44 and a press roller 45. Thefilm 3 sent to the winding chamber 8 is wound by the winding roller 44while being pressed by the press roller 45.

The film 3 can be formed by any well-known solution casting method. Forexample, the TAC film disclosed in Japanese Patent Laid-Open PublicationNo. 2005-104148 can be used. In particular, for the purpose of improvingthe film producing speed, the present invention is applied to the TACfilm formed as follows. Dope containing TAC and a solvent is cast onto acooled peripheral surface of the casting drum to form a casting film.After being cooled and turning into gel, the casting film is solidified.The solidified casting film is peeled as a wet film from the castingdrum and sent to a pin tenter to be dried and form a film. The film iswound in a roll manner and housed to obtain the TAC film. Thereby,according to the present invention, it is possible to efficiently formthe TAC film having excellent optical properties.

Embodiment 2

Although the preceding film 3 a and the trailing film 3 b are spliced toeach other with use of the heat sealer 20 in the splicing section 11 inEmbodiment 1, alternatively, as shown in FIG. 8, an ultrasonic splicer50 can be used to splice the preceding film 3 a and the trailing film 3b.

The ultrasonic splicer 50 mechanically vibrates the film 3, for example,20,000 to 28,000 times/sec at the amplitude of 0.03 mm, to heat and weldthe film 3. The ultrasonic splicer 50 includes two transducers 57, ahorn 59, and a transmitter 53. A permanent magnet 54 is disposed betweenthe transducers 57. A coil 55 is bridged over each of the transducers57. The transmitter 53 causes the coil 55 to drive the transducers 57.The transducer 57 converts electrical vibration to mechanical vibration.The horn 59 amplifies the mechanical vibration caused by the transducer57 to apply energy to the rear end of the preceding film 3 a and thefront end of the trailing film 3 b (vibrate the rear end of thepreceding film 3 a and the front end of the trailing film 3 b) mountedon a mounting base 56. The rear end of the preceding film 3 a and thefront end of the trailing film 3 b are heated by the vibration to bewelded and spliced to each other.

Embodiment 3

Although the preceding film 3 a and the trailing film 3 b are spliced toeach other with use of the heat sealer 20 in the splicing section 11 inEmbodiment 1, alternatively, as shown in FIG. 9, the splicing may beperformed with use of acetone as one of the solvents contained in thedope used in forming the TAC film.

Acetone is applied to the spliced area 28 at the rear end of thepreceding film 3 a by spraying, and then the front end of the trailingfilm 3 b is put on the rear end of the preceding film 3 a. Thereafter,the rear end of the preceding film 3 a and the front end of the trailingfilm 3 b are spliced to each other by the acetone in a press-contactmanner.

Embodiment 4

Although the preceding film 3 a and the trailing film 3 b are spliced toeach other with use of the heat sealer 20 in the splicing section 11 inEmbodiment 1, alternatively, as shown in FIG. 10, a double-sidedsplicing tape 58 having no base of No. 5919ML produced by NITTO DENKOCORPORATION may be used to splice the preceding film 3 a and thetrailing film 3 b. The double-sided splicing tape 58 having no base isadhered to the spliced area 28 of the preceding film 3 a, and thetrailing film 3 b is adhered thereon, to splice the preceding film 3 aand the trailing film 3 b.

Although the TAC film is used as the polymer film according to the firstto fourth embodiments, the present invention is not limited to the TACfilm. The present invention is also applicable to other cellulose esterfilms, for example, cellulose acetate propionate film, and various kindsof polymer films.

Example

The film 3 stretched in the tenter section 5 was subjected to heattreatment for stress relaxation in the relaxation chamber 6. After theheat treatment for stress relaxation, the film 3 shrunk in the filmwidth direction B.

The film 3 obtained by splicing the rear end of the preceding film 3 aand the front end of the trailing film 3 b according to each of thesplicing methods in Embodiments 1 to 4 was subjected to the stretchingprocess and heat treatment for stress relaxation in the off-linestretching device 2. Then, the film width of the spliced area 28 aftershrinkage (heat treatment for stress relaxation) and the film width ofthe peripheral area after shrinkage were measured to obtain resultsshown in Examples 1 to 4. Note that the preceding film 3 a and thetrailing film 3 b were TAC films and had a product width of 80 μm. Thewidth of the film 3 before the stretching was 640 mm, and the width ofthe film 3 after the stretching was 862 mm. After the stretching, inorder to remove the deformed portion of the film 3 caused by being heldby the clips 39, the side edges of the film 3 were cut off by theslitting device 40 such that the width of the film 3 became 660 mm. Thefilm 3 whose side edges were cut away was subjected to heat treatmentfor stress relaxation in the relaxation chamber 6. Moreover, as shown inFIG. 11, the preceding film 3 a and the trailing film 3 b wereoverlapped with each other, and a single-sided splicing tape 60 with abase of No. 31B produced by NITTO DENKO CORPORATION was adhered theretoso as to extend in the film width direction B, thus obtaining the resultshown in Comparative Example. The other conditions of ComparativeExample are the same as those in Examples 1 to 4.

The results of the experiments are shown in Table 1. In Table 1, P(Pass) represents a state of a film after shrinkage, in which thereoccurred no wrinkles in the spliced area 28 and there occurred no tearsin the peripheral area. F (Fault) represents a state of a film aftershrinkage, in which there occurred wrinkles in the spliced area 28 orthere occurred tears in the peripheral area.

TABLE 1 Width of Width of spliced area peripheral State of film afterarea after after shrinkage shrinkage shrinkage Example 1 650 mm 650 mm PExample 2 650 mm 650 mm P Example 3 650 mm 650 mm P Example 4 650 mm 650mm P Comparative 625 mm 650 mm F Example

The film width before shrinkage: 660 mm

For thermal welding of the spliced area 28, the heat sealer 20 was usedin Example 1, the ultrasonic splicer 50 was used in Example 2, theacetone was used in Example 3, the double-sided splicing tape 58 havingno base was used in Example 4. As a result of the experiments, inExamples 1 to 4, the shrinkage amount of the spliced area 28 was equalto that of the peripheral area. The film width of the spliced area 28was equal to that of the peripheral area. Therefore, there occurred nowrinkles in the spliced area 28, and thus leading to excellent results.Further, there occurred no tears in the peripheral area, and thusleading to excellent results.

As described above, the rear end of the preceding film 3 a and the frontend of the trailing film 3 b are spliced to each other by thermalwelding with use of the heat sealer 20 or the ultrasonic splicer 50, bywelding with use of acetone, or by joining with use of the double-sidedsplicing tape 58 having no base, and thereby it is possible to make theshrinkage amount of the spliced area 28 and the shrinkage amount of theperipheral area equal to each other. Accordingly, it is possible toprevent occurrence of wrinkles in the spliced area 28 and tears in theperipheral area. Thus, it is possible to increase the area of the filmcapable of being used as a product in comparison with the films formedin a conventional manner.

Further, since it is possible to make the film width of the spliced area28 after shrinkage and the film width of the peripheral area aftershrinkage equal to each other, the control for preventing meandering ofthe film 3 and transporting the film 3 precisely with use of the EPC canbe secured in comparison with the case where the film width of thespliced area 28 and the film width of the peripheral area are differentfrom each other as shown in FIG. 11.

The present invention is not to be limited to the above embodiments, andon the contrary, various modifications will be possible withoutdeparting from the scope and spirit of the present invention asspecified in claims appended hereto.

1. A splicing method of a polymer film comprising the steps of:overlapping a rear end of a preceding polymer film and a front end of atrailing polymer film; pressing welding heads against a portion in whichsaid preceding and trailing films are overlapped with each other fromeach side in a film overlapping direction while sandwiching said portionbetween said welding heads; and welding said films while keeping atemperature of said welding heads contacting said film at a temperatureequal to or less than a decomposition temperature of said polymer film,to splice said rear end and said front end to each other.
 2. A splicingmethod of a polymer film as defined in claim 1, wherein said polymerfilm is a cellulose ester film.
 3. A splicing device of a polymer filmcomprising: a welding head provided at each side of a portion in which arear end of a preceding polymer film and a front end of a trailingpolymer film are overlapped with each other in a film overlappingdirection; a shifter for moving said welding heads in said filmoverlapping direction between a pressing position and a retractedposition, said welding heads sandwiching and pressing a portion in whichsaid preceding and trailing films are overlapped with each other in saidpressing position, and said welding heads being retracted from saidpressing position in said retracted position; and a heating controllerfor heating said welding heads contacting said preceding and trailingfilms at a temperature equal to or less than a decomposition temperatureof said polymer film after said welding heads is shifted to saidpressing position by said shifter.
 4. A splicing device of a polymerfilm as defined in claim 3, wherein said polymer film is a celluloseester film.
 5. A polymer film stretching method comprising: splicing arear end of a preceding polymer film and a front end of a trailingpolymer film by welding a portion in which said rear end of saidpreceding film and said front end of said trailing film are overlappedwith each other; transporting continuously said polymer film after beingspliced; heating and stretching said transported polymer film by holdingside ends of said polymer film with use of plural clips in a film widthdirection; and subjecting said polymer film after being stretched toheat treatment for stress relaxation while continuously transportingsaid polymer film, such that a shrinkage amount of a spliced area ofsaid preceding and trailing polymer films and a shrinkage amount of anarea around said spliced area becomes approximately equal to each otherin said film width direction.
 6. A polymer film stretching method asdefined in claim 5, wherein said welding is performed with use of heatcaused by a heat sealer.
 7. A polymer film stretching method as definedin claim 5, wherein said welding is performed with use of heat caused byultrasonic vibration of an ultrasonic splicer.
 8. A polymer filmstretching method as defined in claim 5, wherein said welding isperformed with use of a polymer solvent.
 9. A polymer film stretchingmethod comprising: splicing a rear end of a preceding polymer film and afront end of a trailing polymer film by adhering a splicing tape havingan adhesive layer and no base to a portion in which said rear end ofsaid preceding film and said front end of said trailing film areoverlapped with each other; transporting continuously said polymer filmafter being spliced; heating and stretching said transported polymerfilm by holding side ends of said polymer film with use of plural clipsin a film width direction; and subjecting said polymer film after beingstretched to heat treatment for stress relaxation while continuouslytransporting said polymer film, such that a shrinkage amount of aspliced area of said preceding and trailing polymer films and ashrinkage amount of an area around said spliced area becomesapproximately equal to each other in said film width direction.